Generally, the lighting industry has a history which is as old as development of civilization, with close relationship with humankind.
Such the lighting industry has been under continuous progress. Search on light sources, light-emitting methods, driving methods and efficiency improvement has been worked variously.
Light sources typically used in the lighting so far may be incandescent lamps, electric discharge lamps and fluorescent lamps, and they are used for a variety of purposes including home use, landscape use and industrial use.
Among them, a resistive light source such as an incandescent lamp has a low efficiency and a heat generation problem. An electric discharge lamp has problems of a high price and a high voltage. A fluorescent lamp has an environmental disadvantage of mercury usage.
To overcome disadvantages of those light sources, interests in light emitting diodes (LEDs) having advantages of light-emitting efficiency, color variety and design autonomy have been increasing gradually.
A light emitting diode (LED) is a semiconductor element which emits a light when a voltage is applied thereto forwardly. The light emitting diode (LED) has a long usage life, low power consumption, with electrical, optical and physical properties which are proper to mass production and the light emitting diodes (LED) have been replacing the incandescent lamps and fluorescent lamps.